230 Pseudanodonta elongata (2?) in Yorkshire. 
The Wakefield specimens apparently belong to elongata, 
but as the differences between recognised species are small, 
it is desirable to get further and mature specimens before 
pronouncing as to their specific identity. 
Since seeing the specimens from Wakefield, Mr. Hargreaves 
has seen a specimen from Derby, and as the genus closely 
resembles Anodonta superficially, it is probable that it has 
been overlooked and may occur in other localities. 
The umbones give the readiest and most satisfactory way 
of determining the genus. In Anodonta the umbonal striae 
are concentric and more or less semi-circular, in Pseudanodonta 
the markings are distinctly nodulous and are not concentric. 
A further means of distinguishing the two genera, lies in the 
gap in the ventral margin of Psewdanodonta, which does not 
completely close the shell. This method is not absolutely 
certain, as occasionally Anodons are found with the same 

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MARGIN 
peculiarity, but in such cases, reference to the umbones will 
settle the matter. 
On a later occasion, Mr. Firth took over sixty specimens of 
Unionidae from the same locality in which Unio tumidus and 
Anodonta anatina were nearly equal in numbers, a few specimens 
of U. pictorum occurred, whilst there were only three specimens 
of Pseudanodonta, which is therefore scarce. 
The genus Pseudanodonta, of which many species are 
recorded, occurs also in Belgium, France, Germany, Austria, 
Russia, extending as far as Central Asia. In France alone, 
Locard records twenty-seven species, but it must be remembered 
that many of these would be considered by British writers as 
varieties only. 
Along with the Unionidae already mentioned, were also 
found Limnaea pereger, L. palustris, L. stagnalis, Planorbis 
corneus, P. umbilicatus, P. vortex, Physa fontinalis, Bithyma 
tentaculata, Vivipara vivipara, Valvata piscinalis, Neritina 
fluviatilis, Dreissensia polymorpha, Unio pictorum, U. tumidus, 
Anodonta cygnaea (mostly var. anatina), Sphaerium rivicola, 
S. corneum, and Pisidium amnicum. 
Naturalist, 
